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I cannot access ubuntu system on my pc, the error message: "the system is running in low graphics mode" and I tried some commands I searched from internet.

I found out a problems seems there is no available disk space. I used "df" and "du" commands to check, the results are as follow:

du -j --max-depth=1
23G  ./home
3.3G ./usr 
...... 
28G

and

df -Th 
filesystem   Type   size    used   available   use%    mounted on 
/dev/sda5    ext4   68G     68G    0           100%    /

how would I clean up the system for more disk space?

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4 Answers 4

Ok, lets check the man pages:

df - report file system disk space usage

and

du - estimate file space usage

Those two tools were meant for different propose. While df is to show the file system usage, du is to report the file space usage. du works from files while df works at filesystem level, reporting what the kernel says it has available. Continue reading the du manpage support this:

Summarize disk usage of each FILE, recursively for directories.

it says du works with files.

df displays the amount of disk space available on the file system containing each file name argument. If no file name is given, the space available on all currently mounted file systems is shown.

here says that df do not care about the files but the filesystem itself.

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You most probably know that you can remove a file that still in use by some application and for this application it remains available. It because file descriptor in /proc/ filesystem is held open.

So if there are such open descriptors to files already removed, space occupied by them considered as used by df (and df is right), but they can not be taken into account by du due to there are no longer filenames associated with them.

You can find all unlinked but held open files with:

# lsof | grep '(deleted)'
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1  
This just saved me. Had no idea why my disk was full, but du said it was empty. An open file handle for a 8GB file –  Cheyne May 14 at 20:28
    
How can i delete the links? –  Vikas Hardia Aug 22 at 5:46
df

Summarize free disk space

It displays the amount of disk space available .

du

Summarize disk usage.

It displays the amount of disk space used.

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yes, but in the result of "df -Th", it showed 68G used. today morning when i try to access ubuntu system, it still gives "the system is running in low-graphics mode" message, but when i check the memory usage, the "df" and "du" commands shows a reasonable result. But what;s the problem with the "low-graphics mode"? –  user2068965 Apr 12 '13 at 9:41
    
Take a look at This. –  Mitch Apr 12 '13 at 11:10

Simply said:

You ran du without root permissions. So it is not able to check the available space in /proc, /mnt, etc, folders.

df showed the total used & free space respectively.

So when you check the Linux root file system, take the du report as final.

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